Been trying to come up with a solution to the issue that sometimes happens when the indexing rod binds when trying to rotate the carrier plate. Careful observation is that this seems to happen when the plate rotates backward slightly. I noticed that this does not happen if I press down on the flipper during the down stroke of the presses travel, so I came up with a solution.

The spring may serve as a nice remedy, but consider attacking the root cause. The index rod is pulling the shell plate backward. Maybe your index rod flipper is one rotation too tight. Maybe the ejector is not pre-stressed counter clockwise as it should be or its pawl is not shaped properly to engage the indents in the shell plate. I think Richard Lee preferred that the index rod adjustment be set to where the shell plate just does not have any play when locked, yet, IIRC, John Lee advises to have it set to where the shell plate just barely does have some play.